This invention relates to downhole tools used in subsurface well completion and more particularly to tools used to enhance the effectiveness of particulate packing operations.
Gravel packing is a method commonly used to complete a well in which the producing formations are loosely or poorly consolidated. In such formations, small particles (e.g., formation sand or fines) may be produced along with the desired formation fluids, which may cause several problems such as clogging the production flow path, erosion of the wellbore, and damage to expensive completion equipment. Production of particles such as fines can be reduced substantially using a steel wellbore screen in conjunction with particulate material sized to prevent passage of formation sand through the screen. Such particulate material, referred to as “gravel,” is pumped as a gravel slurry and deposited into an annular region between the wellbore and the screen. The gravel, if properly packed, forms a barrier to prevent the fines from entering the screen, but allows the formation fluid to pass freely therethrough and be produced.
Fracturing is another operation that may employ particulate material deposition to advantage. Oil production formations may be stimulated by creating fractures in the production zones to open pathways through which the production fluids can flow to the wellbore. Particulate material known as proppants may be deposited from a slurry into the open fractures to maintain them in their open position.
There are many different arrangements and methods for completing a particulate packing operation. Several gravel packing methods are described in U.S. Pat. No. 6,554,064, which is hereby fully incorporated by reference. Descriptions of fracturing operations may be found in U.S. Pat. No. 6,230,805, which is also hereby incorporated by reference.
In one typical gravel packing installation, a screen is placed in the well bore and positioned within the unconsolidated production zone which is to be completed. The screen is typically connected to a tool that includes a production packer and a cross-over sub, and the tool is in turn connected to a work or production string. The gravel is pumped in a slurry down the work or production string and through the cross-over sub whereby it flows into the annulus between the screen and the well bore. The liquid forming the slurry leaks off into the production zone and/or through the screen which is sized to prevent the gravel in the slurry from flowing it. As the fluid “leaks off” into the perforations into the formation and/or back into the screen, the gravel is deposited in the annulus around the screen where it forms a gravel pack. The size of the gravel in the gravel pack is selected such that it prevents particles such as formation fines from flowing into the well bore with produced fluids.
To be effective, the gravel pack must be devoid of voids. Voids are created when the carrier fluid used to convey the gravel is lost or leaks off too quickly. The carrier fluid may be lost either by passing into the formation or by passing through the screen where it is collected by the end portion of a service tool used in gravel pack applications, commonly known as a wash pipe, and returned to surface. It is expected and necessary for dehydration to occur at some desired rate to allow the gravel to be deposited in the desired location. However, when the gravel slurry dehydrates too quickly, the gravel can settle out and form a “bridge” whereby it blocks the flow of slurry beyond that point, even though there may be void areas beneath or beyond it. This can defeat the purpose of the gravel pack since the absence of gravel in the voids allows fines to be produced through those voids. Therefore, it is important to evaluate the gravel pack after completion to ensure there are no voids.
There has been much prior art relating to the evaluation of gravel packs and density of formations. For example, U.S. patent application publication 2003/0213898 of Storm, et al. describes evaluating gravel packing quality, including the use of nuclear tools for determining the quality of the packing operation after the packing operation has been completed.
While there is much prior art concerning the evaluation of gravel packing operations after their completion, there remains a need to determine not just whether a particular gravel packing job was successful, but how the gravel packing or other particulate deposition operation proceeded and when the particulate depositions occurred along the deposition area.
Additionally, a need exists for gathering data on how particulate depositions proceed during a well completion to provide improved insight and techniques for designing and installing gravel packs, proppants and other particulate depositions.
Furthermore, a need exists for characterizing the flow of fluid(s) injected into a wellbore, such as during gravel packing and other operations.
These needs, as well as other needs, problems, and shortcomings in the art are addressed by the present invention which will now be summarized.